1. Field of the Invention
The present invention relates to micro-electromechanical system (hereinafter referred to as ‘MEMS’) microphones, and more particularly to a multi-floor type MEMS microphone having an improved sensitivity.
2. Description of the Related Art
The MEMS microphone is a capacitive-sensing device that combines two main components, namely a MEMS transducer and an application-specific integrated circuit (hereinafter referred to as ‘ASIC’) chip, in an acoustic housing. Compared to conventional capacitance microphones, the MEMS microphone has the advantages of small size, low power consumption and inert to the interfering factors from the ambient environment, such as temperature change, external vibrations or electromagnetic interference.
FIG. 1 illustrates a conventional package structure 1 that comprises a housing 4 formed by a substrate 2 and a cap 3 mounted on the substrate 2. The cap 3 is employed to protect the MEMS transducer 5 and the ASIC chip 6, both of which are mounted on the substrate 2. However, because of the structural design, the volume of the back chamber 8, which is the space defined by the vibrating diaphragm 7 of the MEMS transducer 5 and the substrate 2, is limited. As a result, the sensitivity may also be limited or unsatisfied. Therefore, the package structure needs to be improved.